1. Field of the Invention
The present invention relates generally to methods of diagnosing and monitoring rheumatic diseases. More particularly, the invention involves several related assays: an assay for the diagnosis of rheumatic disease, an assay for the differential diagnosis of rheumatic disease, an assay for determining the severity of the disease condition and an assay for determining the prognosis of a rheumatic disease.
2. Description of Related Art
Autoimmune diseases are defined as diseases which affect an individual in a manner to cause antibodies to be produced against constituents of the individual's own tissues. Autoimmune diseases may be classified into two broad categories: systemic and organ-specific diseases. The rheumatic diseases include a group of disorders which are within the systemic category. The group includes systemic lupus erythematosus (SLE), mixed connective tissue disease, rheumatoid arthritis (RA), Sjogren's syndrome, and scleroderma.
The cause of RA is unknown. Typically, a patient's clinical and pathological findings and disability are the result of chronic inflammation of synovial membranes. Spontaneous remissions and exacerbations are characteristic of the disease. SLE is a chronic, inflammatory disease of unknown cause which may affect the skin, joints, kidneys, nervous system, serous membranes and other organs. The classic clinical course of the disease is characterized by periods of remissions and relapses.
The systemic nature and relatively nonspecific symptoms of the diseases, particularly SLE and RA, often make the diseases difficult to diagnose and difficult to distinguish. An assay method which would enable the clinician to distinguish and discriminate between SLE and RA is highly desired.
Therapeutic agents such as prednisone, azathioprine, methotrexate and cyclophosphamide are used to treat SLE and other rheumatic diseases. These therapeutic agents, however, produce undesirable side effects and adverse reactions because they act by suppressing the immune system. Therefore, the dosages administered require careful control. In addition, it is possible to discontinue administration of the therapeutic agents when the disease goes into remission, which often happens with SLE, but at the first signs of relapse, the therapeutic agent must be readministered. Thus, there is also a need for a test which can be used to monitor the severity of rheumatic disease so that the dosages of such therapeutic agents can be adjusted, discontinued or resumed.
Traditionally, clinicians use a combination of tests and observations to determine the severity of SLE disease and to adjust drug therapy accordingly. For example, the Lupus Activity Criteria Count (LACC) as described by Urowitz, et al., J. Rheumatol., 11,783 (1983) is frequently used. A LACC score of +2 or greater indicates "active" disease. The presence of each of the following is counted as +1:
1. arthritis; PA1 2. abnormal blood tests: greater than 4000 white blood cells (WBC) per milliliter, CH50 (complement) values of less than 150, or anti-double-stranded DNA antibody titer of greater than 450; PA1 3. new rash, hair loss or oral ulcers; PA1 4. pericarditis; PA1 5. central nervous system involvement: seizures or psychosis; PA1 6. vasculitis; and PA1 7. urine tests: greater than five red blood cells (RBC) per milliliter.
In addition, because glomerulonephritis is cased by SLE, tests of kidney function (such as those for proteinuria and blood urea nitrogen [BUN]) are also used to monitor the severity of disease.
Conventional diagnostic tests for rheumatic diseases, such as SLE, have been based upon the detection of autoantibodies to DNA or to nuclear antigens in the patient's blood. Some of these serum tests are described in the following patents.
U.S. Pat. No. 4,234,563 describes a method for detecting serum anti-DNA antibodies and serum antibodies to extractable nuclear antigens (ENA) in SLE patients. DNA-methylated bovine serum albumin conjugates or thymic extracts are used as capture antigens in such assays to detect serum anti-DNA or anti-ENA antibodies.
U.S. Pat. No. 3,897,212 describes a direct radioimmunoassay for detecting serum anti-DNA antibodies in SLE patients. The serum is incubated with radioactively labelled DNA, and anti-DNA antibodies are measured by determining the amount of radioactive label in the resulting precipitate.
U.S. Pat. No. 3,997,657 describes a method to detect anti-nuclear protein antibodies in serum using a dry slide technique. The method involves fixing thymus cell extract to a glass slide, incubating the serum sample on the slide and indirect immunofluorescent detection of bound antibodies.
U.S. Pat. No. 4,314,987 describes a method of diagnosing rheumatic diseases based upon patterns of fluorescent antinuclear antibodies, followed by testing for anti-DNA or anti-ENA antibodies. More specifically, the method allows for the interpretation of existing tests and is therefore limited by the accuracy of such tests.
U.S. Pat. No. 4,582,793 describes a method for the diagnosis of rheumatic diseases based upon the detection of serum antibodies specific for RNA polymerase I antigen, or its individual subunits.
Such methods require the use of the patient's serum as the test sample for the detection of antibodies. There is a need, therefore, for methods which detect antigens, as well as antibodies, that are characteristic of rheumatic diseases and which use body fluids which are obtainable through noninvasive as well as invasive techniques. The present invention is primarily directed to the detection of such antigens and antibodies in the patient's urine so that the assay can be performed without the need for the invasive collection of test samples.